Biomedical subjects

K Wei

Publications and source records attributed to K Wei.

At least 19 recordsLinked to original sources

PubMed2001

E1A inhibition of radiation-induced NF-kappaB activity through suppression of IKK activity and IkappaB degradation, independent of Akt activation.

Activation of the transcription factor nuclear factor kappaB (NF-kappaB) has been implicated in the protection of cells from apoptosis. We have shown previously that the adenovirus type 5 E1A sensitizes cells to radiation-induced apoptosis by inhibiting NF-kappaB activity. However, the exact mechanism of inhibition is not known. In this study, we compared the activity of inhibitor of nuclear factor-kappaB (IkappaB) kinase (IKK) and the degradation of IkappaBalpha in E1A transfectants and parental human cancer cells after ionizing radiation treatment. We found that radiation-induced IKK activity and IkappaBalpha degradation were inhibited in the E1A transfectants. Recently, Akt has been implicated in NF-kappaB activation. To test whether Akt is regulated by E1A and is involved in radiation-induced NF-kappaB activity, we examined the phosphorylation status of Akt in the E1A transfectants and parental cells and in irradiated cells. The results indicated that radiation induced Akt phosphorylation and that E1A inhibited basal but not radiation-induced Akt phosphorylation. We additionally examined radiation-induced NF-kappaB activity in cells stably transfected with a dominant-negative, inactive Akt and in parental cancer cells treated with a phosphatidylinositol 3-kinase inhibitor, wortmannin. We found that dominant-negative Akt and wortmannin did not block radiation-induced NF-kappaB activity. Thus, our results suggest that inhibition of IKK activity and IkappaB degradation is the predominant mechanism for E1A-mediated inhibition of radiation-induced NF-kappaB activity and that radiation-induced Akt activation cannot be inhibited by E1A and is likely independent of radiation-induced NF-kappaB activity.

Adenoviridae↗

PubMed2001

Noninvasive quantification of coronary blood flow reserve in humans using myocardial contrast echocardiography.

BACKGROUND: We hypothesized that coronary blood flow (CBF) reserve could be quantified noninvasively in humans using myocardial contrast echocardiography (MCE). METHODS AND RESULTS: Eleven patients with normal epicardial coronary arteries (group I) and 19 with single-vessel coronary stenosis (group II) underwent quantitative coronary angiography, MCE, and CBF velocity measurements at rest and during intravenous adenosine infusion. In group I patients, MCE-derived myocardial blood flow (MBF) velocity reserve (2.4+/-0.08) was similar to CBF velocity reserve using a Doppler flow wire (2.4+/-1.1). Patients with a single risk factor had a significantly higher MBF reserve (3.0+/-0.89) than those with >/=2 risk factors (1.7+/-0.22). In group II patients, significant differences were found in MBF velocity reserve in patients with mild (<50%), moderate (50% to 75%), or severe (>75%) stenoses (2.2+/-0.40, 1.6+/-0.65, and 0.55+/-0.19, respectively; P=0.005). A linear relation was found between flow velocity reserve determined using the 2 methods (r=0.76, P<0.001), and a curvilinear relation was noted between the percent coronary stenosis measured using quantitative coronary angiography and velocity reserve using both methods. CONCLUSIONS: CBF reserve can be measured in humans using MCE. This method may allow the noninvasive assessment of coronary stenosis severity and the detection of microvascular dysfunction.

Adult↗

PubMed2001

Cloning and characterization of a novel variant of rat GABA(B)R1 with a truncated C-terminus.

The gamma-aminobutyric acid B receptor (GABA(B)R) belong to the G-protein-coupled receptor superfamily and has been identified as a mediator in the transmission of slow inhibitory neurotransmission in the mammalian central nervous system. Two types of GABA(B)R have been cloned, GABA(B)R1 and R2. GABA(B)R2 is co-expressed with GABA(B)R1 in many brain regions and inwardly rectifying potassium channels are activated by GABA(B)R agonists only upon co-expression of GABA(B)R1 with GABA(B)R2. Several splice variants of GABA(B)R1 receptors have been cloned from rat brain library. Using a rat hippocampal cDNA library, we have isolated a novel cDNA clone of GABA(B) receptor containing an insert of 124 bp between exon 3 and exon 4. This insert occurred between the regions encoding the Sushi domain and leucine binding protein (LBP)-like domain. The insert and subsequent frame shift generated a cDNA that codes for a truncated polypeptide of 239 amino acids lacking the C-terminus. Analysis of the deduced amino acid sequence of the new cDNA clone, termed GABA(B)R1g, showed that it was identical to the first 157 amino acids of GABA(B)R1a, but diverged thereafter. The C-terminal region of GABA(B)R1g contained two cysteine residues. GABA(B)R1g was expressed in both brain and peripheral tissues. Northern blot analysis demonstrated that two transcripts (4.5 kb and 4.0 kb) exist in hippocampus. In addition, studies of hippocampus in developing animals indicated that the expression of GABA(B)R1g is maximal at postnatal day four. GABA(B)R1g could be generated by alternative splicing of the GABA(B)R1 gene.

Alternative Splicing↗

PubMed2001

Cloning and tissue distribution of a novel isoform of the rat GABA(B)R1 receptor subunit.

We have identified a novel splice variant of the metabotropic GABA(B) receptor (R) subunit I, designated GABA(B)R1f, from a rat hippocampus cDNA library screen. GABA(B)R1f shares sequence homology with rat GABA(B)R1a, with the exception of an in-frame deletion of exon 4, resulting in a 21 bp deletion in the coding sequence of the N-terminal extracellular domain. In addition, GABA(B)R1f also contains a 93 bp in-frame insertion in a region of the sequence corresponding to the second extracellular loop and the fifth transmembrane domain, similar to that found in rat GABA(B)R1c. While being ubiquitously (but variably) expressed, reverse-transcription polymerase chain reaction analysis revealed the GABA(B)R1f isoform to be most prevalent in peripheral vs central tissues, suggesting a potential role for this novel isoform in either the mediation of inhibitory transmission in these various tissues, or in as yet defined actions unrelated to central synaptic regulatory mechanisms attributable to GABA(B)R.

Alternative Splicing↗

PubMed2001

Quantification of renal blood flow with contrast-enhanced ultrasound.

OBJECTIVES: The goal of this study was to determine the ability of contrast-enhanced ultrasound (CEU) to quantify renal tissue perfusion. BACKGROUND: The kinetics of tracers used to assess renal perfusion are often complicated by countercurrent exchange, tubular transport or glomerular filtration. We hypothesized that, because gas-filled microbubbles are pure intravascular tracers with a rheology similar to that of red blood cells, CEU could be used to quantify renal tissue perfusion. METHODS: During a continuous venous infusion of microbubbles (SonoVue), regional renal perfusion was quantified in nine dogs using CEU by destroying microbubbles and measuring their tissue replenishment with intermittent harmonic imaging. Both renal blood volume fraction and microbubble velocity were derived from pulsing-interval versus video-intensity plots. The product of the two was used to calculate renal nutrient blood flow. Renal arterial blood flow was independently measured with ultrasonic flow probes placed directly on the renal artery and was increased using dopamine and decreased by placement of a renal artery stenosis. RESULTS: An excellent correlation was found between cortical nutrient blood flow using microbubbles and ultrasonic flow probe-derived renal blood flow (r = 0.82, p < 0.001) over a wide range (2.5 fold) of flows. CONCLUSIONS: Ultrasound examination during microbubble infusion can be used to quantify total organ as well as regional nutrient blood flow to the kidney.

Animals↗

PubMed2001

Mechanism of reversible (99m)Tc-sestamibi perfusion defects during pharmacologically induced vasodilatation.

Reversible perfusion defects on (99m)Tc-sestamibi imaging during hyperemia are thought to occur due to myocardial blood flow (MBF) "mismatch" between regions with and without stenosis. We have recently shown that myocardial blood volume (MBV) distal to a stenosis decreases during hyperemia, resulting in a reversible perfusion defect on myocardial contrast echocardiography (MCE). In this study, we hypothesized that a reversible perfusion defect on (99m)Tc-sestamibi imaging during hyperemia results from the same mechanism. We tested our hypothesis under the following conditions: 1) increases in MBF in the absence of changes in MBV by using direct intracoronary infusion of adenosine (group I, n = 10 dogs); 2) decrease in MBV despite an increase in MBF by left main infusion of adenosine proximal to a noncritical coronary stenosis placed on either coronary artery (group II, n = 13 dogs); and 3) reduction in both resting MBF and MBV by placement of a severe stenosis (group III, n = 7 dogs). In group I dogs, no difference in MBV or (99m)Tc-sestamibi uptake was found between the two coronary beds despite an up to fourfold increase in MBF in one bed with adenosine. In group II dogs, MBV distal to the stenosis decreased during hyperemia despite a twofold increase in mean MBF. A good correlation was found between (99m)Tc-sestamibi uptake and MBV ratios from the stenosed versus normal bed (r = 0.91, P < 0.001). In group III dogs, both MBF and MBV were decreased in the stenosed bed at rest with a good correlation noted between (99m)Tc-sestamibi uptake and MBV ratios from the stenosed versus normal bed (r = 0.92, P = 0.004). We conclude that reversible defects on (99m)Tc-sestamibi during vasodilator stress imaging are related to decreases in MBV distal to a stenosis and not to "flow mismatch" between beds. The decrease in MBV results in reduced (99m)Tc-sestamibi uptake during hyperemia.

Adenosine↗

PubMed2001

Identification of epistatic interactions involved in non-insulin-dependent diabetes mellitus in the Otsuka Long-Evans Tokushima Fatty rat.

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat is an animal model for obese-type non-insulin-dependent diabetes mellitus (NIDDM) in humans. Our present investigation was designed to identify epistatic interactions influencing NIDDM by performing least squares analysis of variance of all pairs of informative markers in 160 F2 progenies bred from an intercross of OLETF and Fischer-344 rats. We identified four interactions between Nidd15/of (chromosome 7) and Nidd16/of (chromosome 14), Nidd15/of and Nidd17/of (chromosome 15), Nidd16/of and Nidd18/of (chromosome 15), and Nidd16/of and Nidd19/of (chromosome 17), which account for a total of approximately 40% of the genetic variation of entire glucose levels after glucose challenge in the F2. The Nidd16/of locus, which is involved in three of four digenic interactions, and the Nidd19/of are likely to correspond to Nidd2/of and Nidd14/of, NIDDM loci previously identified in the F2 by single-QTL model and multiple-QTL model, respectively, while Nidd15/of, Nidd17/of and Nidd18/of loci reflect novel NIDDM loci. An aberrant increase of the entire glucose level due to synergism occurs in the double OLETF homozygote genotype of Nidd15/of and Nidd16/of, and of Nidd16/of and Nidd19/of, as well as in the OLETF homozygote genotypes of Nidd15/of and Nidd16/of, respectively, combined with the heterozygote genotypes of Nidd17/of and Nidd18/of. These findings demonstrate that inter-allelic interactions are likely to be an important component of NIDDM susceptibility.

Animals↗

PubMed2001

Microdosimetry of a 25 keV electron microbeam.

Electron microbeam experiments are planned or under way to explore in part the question regarding whether the bystander effect is a general phenomenon or is restricted to high-LET radiation. Since low-LET radiations scatter more readily compared to high-LET radiations, identifying bystander cells and assessing the potential dose that they may receive will be crucial to the interpretation of radiobiological results. This paper reports on initial calculations of the basic information needed for a stochastic model of the penetration of energetic electrons in tissue-like matter; the model will be used to predict doses delivered to adjacent regions in which bystander cells may reside. Results are presented of calculations of the stochastics of energy deposition by 25 keV electrons slowing down in a homogeneous water medium. Energy deposition distributions were scored for 1-micrometer spheres located at various penetration and radial distances up to 10 micrometer from the point of origin. The energy of 25 keV was selected because experiments are planned for that energy. At 25 keV there is a high probability that the entire electron track will be contained within a typical mammalian cell. Individual tracks are scored because of their primacy; data for higher doses can be obtained by convoluting single-track distributions. The event frequency decreases approximately exponentially after the first micrometer to 1% at about 8 micrometer of penetration. Radially, the 1% contour extends to 3.5 micrometer at a penetration of 5.5 micrometer. The frequency-mean energy deposited decreases from 1.5 to 1 keV/micrometer at a penetration of 3.5 micrometer, then increases back to about 1.5 at a penetration of 6.5 micrometer. The mean energy increases to about 3 keV/micrometer at a radial distance of 8.5 micrometer.

Computer Simulation↗

PubMed2001

[Photocatalytic degradation of bromomethane on sol-gel-derived SO4(2-)/TiO2].

SO4(2-)/TiO2 photocatalysts were prepared by sol-gel method and characterized by X-ray diffraction (XRD), FTIR spectroscopy and N2 sorption analysis applying BET method. Photocatalytic decomposition of CH3Br in air stream was studied over SO4(2-)/TiO2 photocatalysts under the different reaction conditions. The results showed that the addition of SO4(2-) to TiO2 greatly enhanced its structural and photocatalytic properties. The optimum concentration of SO4(2-) on TiO2 was 9% wt and the best calcination temperature was 450 degrees C. Moreover, the sulfated TiO2(SO4(2-)/TiO2) exhibited excellent stability of activity under the moist reaction condition. When the reaction temperature was below 85 degrees C, the reactivity of bromomethane was enhanced with increasing reaction temperatures, and the apparent Arrehenius activation energy was 19.6 kJ.mol-1. In the reaction temperature range of 85 degrees C-105 degrees C, the apparent Arrehenius activation energy was zero.

Catalysis↗

PubMed2000

Specific amelogenin gene splice products have signaling effects on cells in culture and in implants in vivo.

Low molecular mass amelogenin-related polypeptides extracted from mineralized dentin have the ability to affect the differentiation pathway of embryonic muscle fibroblasts in culture and lead to the formation of mineralized matrix in in vivo implants. The objective of the present study was to determine whether the bioactive peptides could have been amelogenin protein degradation products or specific amelogenin gene splice products. Thus, the splice products were prepared, and their activities were determined in vitro and in vivo. A rat incisor tooth odontoblast pulp cDNA library was screened using probes based on the peptide amino acid sequencing data. Two specific cDNAs comprised from amelogenin gene exons 2,3,4,5,6d,7 and 2,3,5,6d, 7 were identified. The corresponding recombinant proteins, designated r[A+4] (8.1 kDa) and r[A-4] (6.9 kDa), were produced. Both peptides enhanced in vitro sulfate incorporation into proteoglycan, the induction of type II collagen, and Sox9 or Cbfa1 mRNA expression. In vivo implant assays demonstrated implant mineralization accompanied by vascularization and the presence of the bone matrix proteins, BSP and BAG-75. We postulate that during tooth development these specific amelogenin gene splice products, [A+4] and [A-4], may have a role in preodontoblast maturation. The [A+4] and [A-4] may thus be tissue-specific epithelial mesenchymal signaling molecules.

Amelogenin↗

PubMed2000

Genetic evidence for obesity loci involved in the regulation of body fat distribution in obese type 2 diabetes rat, OLETF.

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat is an animal model for obese type 2 diabetes in human. Obesity is essential for the onset of type 2 diabetes in this rat. Our present investigation was designed to identify quantitative trait loci (QTLs) contributing to obesity by performing a whole-genome search using 214 F(2) intercross progeny between OLETF and F344 rats. We have identified six QTLs responsible for adiposity indices of fat pads on rat chromosomes 2 (Obs1 for mesenteric fat), 4 (Obs2 for retroperitoneal fat), 8 (Obs3 for mesenteric fat), 9 (Obs4 for retroperitoneal fat), and 14 (Obs5 and Obs6 for retroperitoneal fat), demonstrating that the adiposity indices of individual fat pads were under the control of different genes. As expected, the OLETF allele corresponds to increased adiposity indices for all QTLs, except for Obs3, in which the F344 allele leads to an increase in the index.

Adipose Tissue↗

PubMed2000

Triptolide and chemotherapy cooperate in tumor cell apoptosis. A role for the p53 pathway.

Triptolide (PG490), a diterpene triepoxide, is a potent immunosuppressive agent extracted from the Chinese herb Tripterygium wilfordii. We have previously shown that triptolide blocks NF-kappaB activation and sensitizes tumor necrosis factor (TNF-alpha)-resistant tumor cell lines to TNF-alpha-induced apoptosis. We show here that triptolide enhances chemotherapy-induced apoptosis. In triptolide-treated cells, the expression of p53 increased but the transcriptional function of p53 was inhibited, and we observed a down-regulation of p21(waf1/cip1), a p53-responsive gene. The increase in levels of the p53 protein was mediated by enhanced translation of the p53 protein. Additionally, triptolide induced accumulation of cells in S phase and blocked doxorubicin-mediated accumulation of cells in G(2)/M and doxorubicin-mediated induction of p21. Our data suggest that triptolide, by blocking p21-mediated growth arrest, enhances apoptosis in tumor cells.

Animals↗

PubMed2000

Monte Carlo simulation of single-cell irradiation by an electron microbeam.

A model is presented for irradiation of a cellular monolayer by an electron microbeam. Results are presented for two possible window designs, cells plated on the vacuum-isolation window and cells plated on Mylar above the vacuum-isolation window. Even for the thicker dual-membrane window that facilitates tissue culture and allows the target cell to be centered relative to the electron beam, the majority of the calculated beam spreading was contained in a volume typical of the mammalian HeLa cell line. None of the 10(4) electrons simulated at 25 keV were scattered into the spatial region occupied by neighbors of the target cell. Dose leakage was largest at 50 keV where the mean energy deposited in all neighbors was 21% of that deposited in the target cell. This ratio was reduced to 5% at 90 keV, the highest beam energy simulated. Lineal energy spectra of energy deposition events scored in the nucleus of the target cell became progressively more like the gamma-ray spectrum as the electron beam energy increased. Hence, our simulations provide strong support for the feasibility of a low-LET, single-cell irradiator.

Cell Nucleus↗

PubMed2000

Ribozyme-catalyzed tRNA aminoacylation.

The RNA world hypothesis implies that coded protein synthesis evolved from a set of ribozyme catalyzed acyl-transfer reactions, including those of aminoacyl-tRNA synthetase ribozymes. We report here that a bifunctional ribozyme generated by directed in vitro evolution can specifically recognize an activated glutaminyl ester and aminoacylate a targeted tRNA, via a covalent aminoacyl-ribozyme intermediate. The ribozyme consists of two distinct catalytic domains; one domain recognizes the glutamine substrate and self-aminoacylates its own 5'-hydroxyl group, and the other recognizes the tRNA and transfers the aminoacyl group to the 3'-end. The interaction of these domains results in a unique pseudoknotted structure, and the ribozyme requires a change in conformation to perform the sequential aminoacylation reactions. Our result supports the idea that aminoacyl-tRNA synthetase ribozymes could have played a key role in the evolution of the genetic code and RNA-directed translation.

Acylation↗

PubMed2000

Quantification of the physiological relevance of a coronary stenosis using myocardial contrast echocardiography.

MCE can be used in the catheterization laboratory or in the operating room to provide rapid assessments of the functional significance of a coronary stenosis from direct arterial injections of microbubbles. In the past few years, the development of more stable microbubble contrast agents, and a better understanding of the interactions between ultrasound and microbubbles have led to the development of a truly non-invasive approach to quantify MBF using venous infusions. Furthermore, additional insights into the physiology of coronary stenosis, particularly as it affects MBV, have been obtained using MCE.

Blood Flow Velocity↗

PubMed2000

Relation between regional function and coronary blood flow reserve in multivessel coronary artery stenosis.

In the setting of chronic coronary stenoses, percent wall thickening (%WT) both at rest and during catecholamine stimulation can be abnormal despite normal resting myocardial blood flow (MBF). We hypothesized that this phenomenon is related to abnormal MBF reserve. Accordingly, 15 dogs were studied between 7 and 10 days after placement of Ameroid constrictors around the proximal coronary arteries and their major branches, at a time when collateral development had not yet occurred. %WT and MBF were measured at rest, after 0.56 mg/kg of dipyridamole, and at incremental doses of dobutamine (5-40 microgram. kg(-1). min(-1)). Resting %WT and MBF were normal in all four sham dogs. Resting transmural MBF was normal in all segments in the 11 study dogs, despite reduced (-2 SD of normal) %WT (<30%) in 40 of 82 segments. MBF reserve was reduced (<3) in segments with reduced %WT, and a close coupling was noted between resting %WT and MBF reserve. All segments showed an increase in %WT with dobutamine up to a dose of 20 microgram. kg(-1). min(-1), above which those with abnormal endocardial MBF reserve showed a "biphasic" response. It is concluded that, in the presence of chronic coronary stenoses, abnormalities in resting %WT as well as inducible reduction in %WT during pharmacological stress are related to the degree of abnormal MBF reserve.

Animals↗

PubMed2000

Assessment of resting perfusion with myocardial contrast echocardiography: theoretical and practical considerations.

BACKGROUND: The aim of this study was to perform a quantitative comparison between myocardial contrast echocardiography (MCE) and single-photon emission computed tomography (SPECT) in patients with prior myocardial infarction (MI). We also wanted to determine the optimal method for the intravenous administration of an ultrasound contrast agent in the clinical setting. METHODS AND RESULTS: Seventeen patients with resting perfusion defects in a single vascular territory on SPECT were studied. MCE was performed with intermittent harmonic imaging during continuous infusions of a second-generation ultrasound contrast agent (Sonovue, Bracco Diagnostics) in all 17 patients and after bolus injection in 8 of them. During continuous infusions, the video intensity (VI) ratio between the abnormal and normal myocardium at a pulsing interval (PI) of 8 cardiac cycles correlated well with the activity ratio between these segments on SPECT (r = 0.73, P <.01). When information regarding microbubble velocity (MV) denoted as change in VI with increasing PIs was added, the correlation with SPECT activity ratio improved (P <.05) significantly (r = 0.87, P <.0001). Higher microbubble doses resulted in higher VI during continuous infusions with good myocardial opacification and no far-field attenuation until the highest dose was reached. With bolus injections, the VI ratio between the abnormal and normal myocardium at PI of 1 and 5 cardiac cycles showed a modest correlation (r = 0.46 and r = 0.48, respectively, P <.05) with activity ratios between these regions on SPECT. When a dose of microbubbles administered as a bolus produced adequate myocardial opacification, it invariably resulted in far-field attenuation. CONCLUSIONS: In patients with prior MI, quantitative assessment of resting perfusion defects on MCE correlates well with regional activity on SPECT. Continuous infusions offer an advantage over bolus injections because they can provide an assessment of both relative VI and MV. Adjustment of the microbubble infusion rate produces adequate myocardial opacification without attenuation.

Coronary Circulation↗

PubMed2000

[Assessment of the effects of dipyridamole and dobutamine on coronary microcirculation using myocardial contrast echocardiography].

OBJECTIVES: To evaluate the effects of dipyridamole and dobutamine on myocardial blood flow (MBF) and myocardial blood volume (MBV), and their ability to detect non-flow-limiting coronary stenoses with myocardial contrast echocardiography (MCE). METHODS: Thirteen closed-chest dogs were studied at 7-10 days after placement of ameroid constrictors around proximal coronary arteries and their branches. MBF was measured with radiolabeled microspheres and myocardial plateau video intensity (VI, which indicates relative MBV) and microbubble velocity (beta) were measured with MCE at rest, after dipyridamole (0.56 mg/kg), and during peak dobutamine dose (30-40 micrograms.kg-1.min-1). RESULTS: The effects of both agents on MBF were similar in abnormal and normal segments. Plateau VI increased more and beta increased less with dobutamine than dipyridamole (P < 0.05), but the plateau VI ratios and beta ratios between abnormal and normal segments were almost identical during both drugs (P < NS), resulting in similar perfusion defects. Excellent linear relations were found between the plateau VI ratio or beta ratio and MBF (derived from radiolabeled microspheres) ratio from abnormal and normal beds during dipyridamole and dobutamine. CONCLUSION: Although the effect of dipyridamole and dobutamine on MBV is different, they unmask MBF reserve to a similar extent. Thus, the quantification of stenosis severity is identical using both agents with MCE.

Animals↗